Silver triflate

Dibenzotellurophene, [RhCp Cl2]2, and silver inflate yield the ri (Te) coordinated product 329 [97JCS(D) 1579]. In the absence of silver triflate, species 330 is formed. Reduction of 329 with dicyclopentadienyl cobalt results in 331. If, however, this process is conducted in the presence of Fe3(CO)i2, ring-opened products 332 and 333 are isolated. 

Pyridyl)benzothiazole with [Re(CO)5X] (X = Cl, Br) forms the chelate structures 18 (X = C1, Br) (01ICA(314)91). With silver triflate, dehalogenation occurs followed by formation of 18 (X = OTf). The latter refluxed in acetonitrile gives the cationic complex of stoichiometry [Re(CO)3L(AN)](OT0-... 

Thioglycosides containing free OH groups readily tolerate silver triflate-pro-moted glycosylations with glycosyl bromides and chlorides, and also tin(II) chloride-silver perchlorate-activated glycosylation, and several examples have... 

Disarmed as well as armed (see Section V and Scheme 9) phenyl selenoglycosides are reported to be activated by silver triflate in the presence of potassium or silver carbonate in the presence of armed ethyl thioglycoside acceptors, to produce ethyl thiodisaccharides in excellent yields. 

Glycosyl bromides can be used as donors in the presence of phenyl se-lenoglycoside acceptors, using silver triflate as a promoter in the presence of collidine. 

Coupling of 237 with the protected 2-amino-2-deoxy-o -D-glucopyranosyl bromide (348) in dichloromethane in the presence of silver triflate afforded a diastereoisomeric mixture. The isomer related to the natural one was depro-tected with sodium in liquid ammonia, to give the carba-trehalosamine... 

Reaction of368 with hepta-O-acetyl-a-maltosyl, -cellobiosyl, and -lacto-syl bromide in 1,2-dichloroethane in the presence of silver triflate gave the respective carba-tetrasaccharides, including validamycin D. 

The bicyclo[6.1.0]nonatriene 46 is transformed to the 8,8-dihydroindene on treatment with a catalytic amount of [Rh(CO)2Cl]2 [24], The stereoselectivity depends on the reaction temperature. [5 + 2]cycloaddition of vinylcyclo-propanes 47 with alkynes is catalyzed by RhCl(PPh3)3 in the presence of silver triflate to give seven-membered rings 48 [25]. (Scheme 17 and 18)... 

Some N-glycosides have been synthesized as nucleoside analogues by Vilarrasa and co-workers <1996TL901>, the result is shown in Scheme 8. The starting compound, [l,2,4]triazolo[5,l-c][l,2,4]triazine-4(l//)-one 54, was reacted with tri-0-benzoyl-/3-diribofuranosyl bromide under two different reaction conditions. In the presence of silver triflate at low temperature, the zwitterionic 2-substituted compound 55 was obtained, whereas under reflux conditions in acetonitrile the neutral 1-substituted compound 56 was formed. 

Representative Procedure for Lewis Acid Promoted Clycosylation with TOPCAT Glycosyl Donor Using Silver Triflate [335]... 

S-Benzoxazolyl (SBox) and, especially, S-thiazolinyl (STaz) moieties are sufficiently stable for use in anomeric protection. These derivatives can, however, be activated under mild conditions using silver triflate [114-118]. 

Several other examples have been reported in which thioglycosides were used as glycosyl acceptors. Thus, thioglycosides containing free hydroxyls can be coupled chemoselectively with glycosyl bromides and chlorides in the presence of silver triflate or tin(II) chloride-silver perchlorate as the promoter system [12,53,56,162,218-221]. 

A variety of other activating systems have been employed for the promotion of sulfoxide-based glycosylation reactions, but none have been studied to the same extent as the triflic-anhydride-mediated reaction [86]. One of the most potent activators, benzenesulfenyl triflate, a by-product of the activation with triflic anhydride, has been shown to bring about rapid conversion of sulfoxides into glycosyl triflates [280]. Unfortunately, this reagent is unstable and has to be prepared in situ from silver triflate and benzenesulfenyl chloride. 

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